Permanent magnet core galvanometer



Oct. 5, 1965 BYONG HO AHN ETAL 3,210,664

PERMANENT MAGNET CORE GALVANOMETER 2 Sheets-Sheet 1 Filed Oct. 10, 1960 FIG. I

FIG.2

INVENTOR. BYONG HO AHN AND SEYMOUR CUKER WTTORNEY 2 Sheets-Sheet 2 AT FORM Oct. 5, 1965 BYONG HO AHN ETAL PERMANENT MAGNET CORE GALVANOMETER Filed Oct. 10, 1960 Q) a? x N g @1? s FIG United States Patent 3,210,664 PERMANENT MAGNET CORE GALVANOMETER Byong Ho Aim and Seymour Cutter, Manchester, N.H., asslgnors to Van Norman lniilustries, Inc., Manchester, N.H., a corporation of Massachusetts Filed Oct. 10, 1960, Ser. No. 61,546 3 Claims. (Cl. 324-451) This invention relates to electrodynamic galvanometers and, more specifically, to light meters.

One of the objects of the invention is to reduce cost of construction and assembly by reducing the number of elements of the galvanometer and, more specifically, by making an annular pole piece cooperating with a diametrical gap-forming core of one piece with a diametrical magnetic bridge.

Another object of the invention is to arrange the core at an angle with respect to the bridge which preferably also represents the Zero position of the galvanometer coil.

Still another object of the invention is to fasten the core on a non-magnetic bridge member parallel to the magnetic bridge member and to provide that non-magnetic bridge member with peripheral end projections serving as a stop for the coil movement.

Still another object of the invention is to provide a conductive washer between one end of the coil shaft and its bearing, having a radial extension supporting a dielectrio sleeve consisting, for example, of a glass bubble, which serves as a lead-through for at least one of the coil connections.

These and other objects of the invention will be more fully apparent from the drawings annexed herewith in which FIGS. 1 and 2 represent top views on different horizontal planes of a light meter assembly and FIG. 3 a corresponding bottom view, while FIG. 4 represents a side elevation section, of that light meter assembly which embodies certain principles of the invention.

As apparent from FIGS. 1, 2, 3 and 4, an annular pole piece or ring is indicated at 1, cooperating with a core 2 to form diametrical air gap 3 through which the field lines are closed in otherwise well-known manner permitting the movement therein of a galvanometric coil 4.

Annular pole piece 1 is magnetically closed by a diametrical bridge plate or strip 5 at the lower side of pole piece 1. Another non-magnetic, preferably brass, diametrical bridge plate or strip 6 supported in grooves 7 on the other and upper side of pole piece 1, serves to hold a permanent magnet or core 2 by means of prongs 8 which are of one piece with, and projecting from, non-magnetic bridge plate 6.

Bridge plate 6 fits into a groove 9 of core 2 thereby determining a predetermined angular position of core 2 relative to bridge plate 6 which in turn is parallel to magnetic bridge 5, and this also determines the rest position of galvanometer coil 4 and galvanometer needle 10 supported thereon, because in its rest position coil 4 will tend to be substantially parallel to the field lines closing through core 2, ring 1 and bridge plate 5, in a direction parallel to the longitudinal extension of core 2.

Diametrical non-magnetic bridge 6 has circumferential extensions 11, 12 in the plane of plate 6 serving as stops for the movement of galvanometer needle 10. Bridge 6 in turn is held in its place by a second non-magnetic member 1 parallel thereto and also attached to annular pole piece 1 on top of bridge 6. This attachment is realized, for example, by providing on the top edge of annular pole piece 1, slots 14 so dimensioned that the corresponding ends of non-magnetic bridges 6 and 13 can be firmly fixed on pole piece 1 by simply being pressed into slots 14.

Thus assembly and accuracy of assembly, as well as accuracy of operation of the device, are assured with a minimum of elements and handling.

Galvanometric coil 4 and needle 10 are held rotatable between tips 15, 16, preferably of a common shaft, passing through core 2, and tips 15, 16 are in turn supported on recessed bearings 17, 18 formed in or supported on central adjustment screws schematically indicated at 17, 18, respectively. Screws 17, 18 are provided in corresponding central portions of magnetic and non-magnetic bridge members 5 and 13, respectively, on opposite sides of annular pole piece 1.

Spiral springs 19, 20 oppositely acting and attached between shaft ends 15, 16, respectively, and stationary points or parts (not shown) of the meter in otherwise well-known manner, serve to stabilize and dampen the movement of galvanometer needle 10; they also serve to connect one end of coil 4 to an outside terminal (not shown).

One end of coil 4 is connected by means of a wire lead 21 which first is passed insulatingly, for example, by way of a glass bubble 22 which in turn is supported in an opening of lateral extension 23 of a washer 24. Thereafter lead 21 is held between top bridge 13 and a prong 25 which is of one piece with, and projecting from top bridge 13.

Galvanometer needle 10 is provided with one extension arm 28 and two perpendicular cross arms 26 and 27, which serve to balance its movement in other than horizontal positions of its plane of motion. Adjustable member 29 may be moveable along arm 28 and wing plate 30 attached to the other end of needle 10 may serve as a camera shutter or other control element actuated by galvanometer needle 10 under control of current flowing through its coil 4 and derived, for example, from a photoelectric cell which is arranged to control the shutter openmg.

The invention is not limited to the exact shape, and arrangement of the magnetic and non-magnetic, and electrically conducting and insulating elements shown and described, nor to the relative arrangements and attachments in space and circuit-wise of these elements or of any other element shown and described, but may be applied in any appropriate form or manner whatsoever without departing from the scope of this disclosure.

We claim:

1. A galvanometer structure comprising, in combination, a generally hollow cylindrical magnetic pole piece formed with an integral magnetic bar diametrically spanning one open end thereof, a first non-magnetic bar support member secured to and diametrically spanning the opposite end of said hollow cylindrical pole piece, a generally rectangular permanent magnet core secured to said support member and disposed diametrically within said hollow cylindrical pole piece, said permanent magnet core being formed with cylindrical end faces spaced from and confronting the inner surface of said hollow cylindrical pole piece thereby defining a pair of diametrically opposite arcuate air gaps, said permanent magnet core having its longer dimension angularly offset from said first non-magnetic support member, a second non-magnetic bar support member diametrically spanning the opposite end of said hollow cylindrical pole piece and spaced outwardly from said first non-magnetic support member, each of said bar members longitudinally extending in the same diametric plane across said cylinder, a generally rectangular galvanometer coil pivoted for rotation upon said integral magnetic bar and said second non-magnetic support member and embracing both said permanent magnet core and said first non-magnetic support member, resilient means for normally maintaining said coil at rest with opposite ends thereof within said air gaps, a pointer affixed to said coil in the region between said first and second support members and extending outwardly of said galvanometer structure, and coupling means for applying an electric current to said coil.

2. A galvanometer structure in accordance with claim 1 wherein said first non-magnetic support member is formed with rigid means extending into the path of rotation of at least a portion of said coil to define stops limiting the angular movement of said coil said stops being in the plane of said first non-magnetic support bar and circumferentially extending within said cylindrical pole piece.

3. A galvanometer structure in accordance with claim 1 wherein said hollow cylindrical magnetic pole piece is formed with a pair of diametrically opposed slots in the end opposite said magnetic bar, the ends of said first and second non-magnetic support members being rigidly se- 4 cured to said cylindrical pole piece by attachment within said slots.

References Cited by the Examiner UNITED STATES PATENTS 15 WALTER L. CARLSON, Primary Examiner.

ELI J. SAX, Examiner. 

1. A GALVANOMETER STRUCTURE COMPRISING, IN COMBINATION, A GENERALLY HOLLOW CYLINDRICAL MAGNETIC POLE PIECE FORMED WITH AN INTEGRAL MAGNETIC BAR DIAMETRICALLY SPANNING ONE OPEN END THEREOF, A FIRST NON-MAGNETIC BAR SUPPORT MEMBER SECURED TO AND DIAMETRICALLY SPANNING THE OPPOISTE END OF SAID HOLLOW CYLINDRICAL POLE PIECE, A GENERALLY RECTANGULAR PERMANENT MAGNET CORE SECURED TO SAID SUPPORT MEMBER AND DISPOSED DIAMETRICALLY WITHIN SAID HOLLOW CYLINDRICAL POLE PIECE, SAID PERMANENT MAGNET CORE BEING FORMED WITH CYLINDRICAL END FACES SPACED FROM AND CONFRONTING THE INNER SURFACE OF SAID HOLLOW CYLINDRICAL POLE PIECE THEREBY DEFINING A PAIR OF DIAMETRICALLY OPPOSITE ARCUATE AIR GAPS, SAID PERMANENT MAGNET CORE HAVING ITS LONGER DIMENSION ANGULARLY OFFSET FROM SAID FIRST NON-MAGNETIC SUPPORT MEMBER, A SECOND NON-MAGNETIC BAR SUPPORT MEMBER DIAMETRICALLY SPANNING THE OPPOSITE END OF SAID HOLLOW CYLINDRICAL POLE PIECE AND SPACED OUTWARDLY FROM SAID FIRST NON-MAGNETIC SUPPORT MEMBER, EACH OF SAID BAR MEMBER SLONGITUDINALLY EXTENDING IN THE SAME DIAMETRIC PLANE ASCROSS SAID CYLINDER, A GENERALLY RECTANGULAR GALVANOMETER COIL PIVOTED FOR ROTATION UPON SAID INTEGRAL MAGNETIC BAR AND SAID SECOND NON-MAGNETIC SUPPORT MEMBER AND EMBRACING BOTH SAID PERMANENT MAGNETIC CORE AND SAID FIRST NON-MAGNETIC SUPPORT MEMBER, RESILIENT MEANS FOR NORMALLY MAINTAINING SAID COIL AT REST WITH OPPOSITE ENDS THEREOF WITHIN SAID AIR GAPS, A POINTER AFFIXED TO SAID COIL IN THE REGION BETWEEN SAID FIRST AND SECOND SUPPORT MEMBERS AND EXTENDING OUTWARDLY OF SAID GALVANOMETER STRUCTURE, AND COUPLING MEANS FOR APPLYING AN ELECTRIC CURRENT TO SAID COIL. 